1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium in which color images may be formed and erased reversibly based on color-developing reactions between electron-donating coloring compounds and electron-accepting compounds by controlling applied thermal energies, and also relates to a reversible thermosensitive recording label, a reversible thermosensitive recording member, an image processing apparatus and a process which employ the reversible thermosensitive recording medium respectively.
2. Description of the Related Art
Previously, thermosensitive recording media which utilize reactions between electron-donating coloring compounds (hereinafter, sometimes referred as “coloring agent”) and electron-accepting compounds (hereinafter, sometimes referred as “color developer”) are well-known, and have been broadly utilized as output papers of facsimiles, word processors and scientific instrumentation apparatuses, with an advance of office automation, and nowadays in magnetic thermosensitive cards such as a pre-paid card and point card.
However, since such thermosensitive recording media are irreversible and disposable after their usages, an environmental issue has been derived. Accordingly, from the nowadays view point on recycle, a reversible thermosensitive recording composition and reversible thermosensitive recording medium that employ a composition in the thermosensitive layer is proposed, in which an organic phosphorus compound containing a long-chain fatty hydrocarbon group, fatty carbonyl acid compound, or phenol compound as a developing agent is combined with a leuco dye as a color former (see Japanese Patent Application Laid-Open (JP-A)No. 5-124360). Also a reversible thermosensitive recording composition is proposed, in which a phenol compound of certain structure having a long-chain fatty hydrocarbon group is employed as a developing agent (see JP-A No. 6-210954).
However, when printing and erasing are repeatedly carried out on the reversible thermosensitive recording media in the actual condition, such problems may appear as decrease of image density, blowing trace, flaw, and erasing remainder. Consequently, the excellent developing-erasing properties owing to the coloring agent and color developer incorporated in the reversible thermosensitive recording media have not been sufficiently demonstrated.
In order to resolve these problems concerning the reversible thermosensitive recording media, such an approach was made from the mechanical standpoint that the load on the recording face should be as low as possible. For example, a means for increasing the resistivity is proposed in which the smear is removed by water or cleaning solution in the erasing step (see JP-A No. 2001-301331); and an erasing process was proposed in which a photothermo-transverse tape is utilized (see Japanese Patent (JP-B)No. 3194398, JP-A No. 2001-315367).
However, there arise some difficulties in these proposals such as additional consumables are required, and the instruments come to complex and expensive.
As a result, an improved durability is required in the reversible thermosensitive recording medium itself, for example, the addition of silica is proposed of which the surface is treated with an organic silane compound (see JP-B No. 3315831). However, in the proposal, such matters appear that the erasing remainder does not decrease to a satisfactory level along with the repeated printing-erasing, and crazings occur on the printed areas.
Further, similar proposal have been made in which a pigment with surface treatment is added to one of the thermosensitive layer, protective layer and anchor layer (see JP-A No. 10-264521). However, when the pigment with surface treatment is added to the protective layer, the distortion caused by repeated printings may not be eliminated thereby crazings may be induced. On the other hand, when the pigment with surface treatment is added to the thermosensitive layer and anchor layer, such deficiencies arise that the image clearness comes to down, and the images turn to obscure.
As aforementioned, the reversible thermosensitive recording media have not been attained yet, which are free of image degradation due to mechanical damages even after the repeated recording and erasing. Accordingly, such improvements for the reversible thermosensitive recording media are demanded as soon as possible.